Molecular characterization of organic aerosols over the Tibetan Plateau: Spatiotemporal variations, sources, and...

Organic aerosols have profound and far-reaching influences on the Earth's climate, ecosystems, environmental quality, and public health. Elucidating the precise composition and sources of these aerosols over the Tibetan Plateau, a region highly sensitive to climate change and vulnerable to ecosystems, is critically important. Sixteen organic molecular tracers in aerosols were quantified using solvent extraction-BSTFA derivatization, and GC/MS analysis at six sites over the Tibetan Plateau during 2014 and 2016. Average total tracer concentration was 32.5 ± 20.1 ng m^-3. The highest levels of biomass burning tracers (anhydrosugars and aromatic acids) were found at southeastern Tibetan Plateau site Yulong (20.8 ± 21.3 ng m^-3) followed by the western site Ngari (13.3 ± 10.6 ng m^-3). Biomass burning tracers decreased from southern sites like Everest (9.50 ± 10.5 ng m^-3) to northern aeras such as Laohugou (2.59 ± 2.19 ng m^-3). Biomass burning tracers peaked in non-monsoon seasons while primary saccharides and sugar alcohols predominated during monsoon months. Using tracer-based methods, biomass burning contributed 0.4%-8.4% of organic carbon over the plateau, with higher non-monsoon contributions (3.6% ± 3.7%). Backward air mass trajectories and fire spots indicated South Asian biomass burning impacts on organic aerosols at western, southern, and southeastern Tibetan Plateau sites, particularly in non-monsoon periods. Fungal spores and plant debris comprised 0.6%-6.3% and 0.3%-1.2% of organic carbon respectively, with higher monsoon contributions (4.2% ± 4.7%) of fungal spores. Secondary organic carbon was estimated to contribute substantially (45.5%-73.5%) over the plateau but requires further investigation. These results provide insights into pollution mitigation and the assessments of climate and ecology changes for the Tibetan Plateau.